Mercury switch



` April 25, 1939. C. H, LARsoN MERCURY SWITCH Filed oct. 1o, 1935 2 Sheets-Sheet l M507@ 'MMM/m April 25, 1939. c. H. LARsoN MERCURY SWITCH 2 Sheets-Sheet 2 Filed Oct. l0, 1935 IE5, I

Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE MERIURY SWITCH Application October 10, 1935, Serial `No. 44,398

8 Claims.

'I'here are many situations in which it is desirable to close an electrical circuit for a predetermined period of time upon the happening of some event, either temporary or continuing. The happening of the event may readily be made to operate a relay coil, but a diiculty arises in obtaining a switch element to associate with the coil to accomplish the desired action of closing an electrical circuit for a predetermined period. Then, too, it is desirable to associate a circuit with the switch so that the action oi the switch will be the same regardless of the duration of the event, i. e. the energization or de-energization of the relay coil.

These desiderata constitute some of the more important objects of this invention, others being apparent as the disclosure proceeds and the description is read in conjunction with the accompanying drawings, in which Fig. 1 is a view showing a pull-up switch made in'accordance with this invention;

Fig. 2 is a fragmentary view showing the relationship of the switch parts at lthe moment when the coil is de-energized;

Fig. 3 shows the relationship of the switch parts after the electrical circuit through the switch element has been closedfor a pedetermined period;

Fig 4 shows an electrical circuit which may be associated with a relay of the type shown in Fig. 1

in order to make the switch perform its intended function even though the break in the coil circuit is only momentary.

Fig. 5 is a view corresponding to Fig.A 1 but showing a pull-down switch;

Fig, 6 is a fragmentary view showing the relationship of the switch parts imm'ediately after the coil has been energized;

Fig. 7 shows the relationship of the switch parts after the circuit through the switch has been closed for a predetermined period; and

Fig. 8 illustrates a circuit which may be used with a switch of the type shown in Fig. 5 in order to have the switch perform its intended function either when the coil is momentarily energized or permanently energized.

It will be understood that the illustration and description of preferred forms of the invention are for the purpose of complying with Section 4888 of the Revised Statutes and the appended claims are to be construed as broadly as the prior art will permit.

Referring first to Fig. 1, a relay coil is indicated at I0 having a core opening I I in which a mercury switch I2 is mounted. A magnetic circuit I3 is associated with the coil and switch for fixing the position of 'the operating air gap indicated at I4. Details of the magnetic circuit may be found in my Patent No. 1,967,951 issued July 24, 1934, and further description is deemed unnecessary here.

'I'he switch I2 comprises a switch envelope I5 having a somewhat enlarged base I6 through which wires I'l,'I8 and I9 are sealed, the wires 'preferably being of molybdenum or tungsten.

Glass sleeves 20 are fused to the wires I1 and I9 10 for a portion of their length leaving bared por- .tions 2| and 22 serving as electrodes. It will be observed that the insulating sleeve 20 surrounding the wire I9 is somewhat longer than the corresponding sleeve around the wire Il, this having the eiect of positioning the electrode 22 slightly above the electrode 2|.

The switch envelope contains a mercury fill 23, the level of which is adapted to be shifted by the displacing action of an armature or plunger 20 2l comprising an elongated glass thimble 25 having its upper portion surrounded by an iron sleeve 2B, the two parts being held together by springs 21 telescoped over the projecting ends of the thimb1e25. The springs also serve the additional function of clamping guide washers 28 to the top and bottom of the sleeve 26, these guide washers having lugs 29 engaging the side walls of the switch envelope to guide theA movements of the armature as it moves within the switch envelope.

The thimble 25 has a small opening 30 in its top Wall and this is closed with a plug 3| of porous material, such as lavite, alundum, or other commercial ceramic material. The plug is sealed to the thimble 25 so that no gas may pass from the interior of the thimble to the exterior without going through the porous plug 3L After the switch parts have been assembled, the switch envelope is evacuated and a suitable gas fill inserted. 'I'he iill may be helium, hydrogen or the like, or a combination of inert gases.

When the coil is energized, the armature assumes the position such as shown in Fig. 1, inwhich the lower end of the thimble 25 is slightly above the mercury illl. The electrode I8 is covered with mercury but the electrodes 2I and 22 are above the mercury. In this position of the velements composing the switch, the mercury is at its low level. f

When the coil I0 is de-energized, the armature falls tothe position shown in Fig. 2, the downward movement of the armature trapping gas within the thimble 25, thereby causing the mercury level on the exterior of the thimble to immediately rise to a position substantially above iii the electrodes 2| and 22. As gas slowly escapes from the interior of the thimble through the porous block 3|, the mercury level within the thimble gradually rises and that on the outside of the thimblegradually falls until after a predetermined time, the electrode 22 will be uncovered, and shortly thereafter, the electrode 2| becomes uncovered. When the armature is in this position, and the pressures of the gas both exteriorly and interiorly of the amature have been equalized, the mercury is at its high level. Assuming that the electrodes 2|, 22 control diilerent load circuits (see Mg. 4) and the electrode I8 is used as a common lead, the switch functions to close both load circuits as soon as the coil ID is deenergized, and then after a given lapse of time, open first the load circuit associated with the electrode 22 and then the load circuit associated with the electrode 2|.

There may be times when it is desirable to have the switch energize the load circuits for a period determined by the time delay element 3| even though the break in the coil circuit is only momentary. En other words, if the coil I in Fig. 1 is momentarily de-energized, the armature will fall to the position shown in Fig. 2, but before it has had an opportunity to equalize the outside and inside mercury levels as determined by the time delay element 3|, the coil has again picked up the displacer to the position shown in Fig. i (the mercury carried up within the thimble 25 immediately falling away from the thimble as soon as the outside mercury level falls below the lower end oi the thimble).

In order to permit the switch |2 to perform its intended function for a momentary deenergization of the coil I 0, the circuit shown in Fig. 4 may be used. As shown, the coil I0 has a double winding, one part |0a being placed so that it tends to lift the displacer out of the mercury and the other part Illb being placed so that it tends to hold the displacer depressed within the switch envelope. The coil Illa is the main operating coil and is connected to a suitable source of current V35, and the device which interrupts the circuit through the coil Illa is indicated at 36. The coil IOb is connected in series with the switch I2, i. e. one end is connected to the source 35 (or some other source) and the other end is connected to the ce-ntral electrode I8. The electrodes 2| and 22 are connected to the other side of the source through loads 31a and 31h, respectively.

It is obvious that with this arrangement, a momentary de-energization of the coil Ilia will cause the displacer to drop and bridge the electrodes I8 and 2|, 22. This energizes the holding coil |017 which maintains the displacer in its depressed position until the time delay element 3| has had an opportunity to perform its function. As soon as the electrode 2| is uncovered, the circuit through the coil IDb is opened, and the switch is again subject to the main operating coil IIla. It will be understood that the winding of the coil Ib is sufficient to hold the displacer depressed even though the coil Ilia is also energized.

The type of switch shown in Figs. -7 inelusive, is very similar to the one shown in Figs. 1-3 inclusive, the principal diierence being that the coil I0 must be energized in order to actuate the switch here designated 40. The air gap 4| in the magnetic circuit is somewhat 'lower than the corresponding air gap I4 shown in Fig. 1 and the displacer I2 is held in its raised position by the buoyancy of the mercury fill 23. Since the force of buoyancy is used tohold the displacer in its uppermost position, it is necessary to provide an opening 43 in the side of the thimble 25 so that when thev armature rises from the position shown in Fig. 'I to that shown in Fig. 5,.the mercury carried up within the thimble 25 will quickly leave the thimble as soon as the outside mercury level falls below the opening 43. .Except for the diierences noted above, the relay shown in Figs. 5-7 inclusive is substantially the same as the one in Figs. 1-3, and the same reference characters will be used to designate corresponding parts.

In order to adapt the switch to a situation where the coil I0 is only momentarily energized, a circuit such as shown in Fig. 8 may be used. The circuit is essentially the same as that shown in Fig. 4 with the exception that the coils I0a and IIIb may be wound on the same spool and operate with the same air gap whereas in Fig. 4, the coil Ib was necessarily placed below the coil Illa.

What I claim is:

1. In a mercury switch relay, the combination of a coil, a mercury switch associated with the coil comprising a switch envelope, a mercury iill, an armature adapted to move in response to the coil to displace more or less mercury according to the direction of movement, a gas iill, a plurality of electrodes projecting into the envelope, one of which is positioned exteriorly of the armature above the high mercury level, and means or closing the circuit through said one electrode and one other for a predetermined time in response to said coil, said means including a time delay element associated with the armature.

2. In a mercury switch relay, the combination of a coil, a mercury switch associated with the coil comprising a switch envelope, a mercury fill, an armature adapted to move in response to the coil to displace more or less mercury according to the direction of movement, a gas fill, a plurality o! electrodes projecting into the envelope, one of which is positioned exteriorly of the armature above the high mercury level, and means for closing the circuit through said one electrode and one other for a predetermined time in response to said coil, said means including a time delay element associated with the armature and adapted to compress gas within the armature as the displacer is lowered.

3. In a mercury switch adapted to close an electrical circuit for a predetermined length of time in response to a relay coil, a switch envelope, a mercury fill, a plurality of electrodes within the envelope, a displacer reciprocable within the envelope for changing the mercury level with respect to at least one of said electrodes, said displacer comprising a thimble having a. porous wall in its upper portion and an iron sleeve telescoped over the thimble, at least one of said electrodes being positioned exteriorly of the displacer and above the level of the mercury when the displacer is in its lowermost position and all parts of the mercury fill are in equilibrium.

4. In a mercury switch relay, the combination of a coil, a mercury switch associated with the coil comprising a switch envelope, a mercury iill, a displacer reciprocable within the envelope in response to the coil to displace more or less mercury accordingto the direction of movement, a gas fill, a plurality of electrodes projecting into the envelope, one of which is positioned exteriorly of the displacer above the high mercury level. and means for closing the circuit through said one electrode and one other for a predetermined time in response to said coil, said means including-an inverted cup-shaped portion o! the displacer equipped with a time delay element.

5. In a mercury switch relay, the combination of a coil, a mercury switch associated with the coil comprising a switch envelope, a mercury till, a displacer reciprocable within the envelope in response to the coil to displace more or less mercury according to the direction of movement, a gas fill, a plurality of electrodes projecting into the envelope, one of which is positioned exteriorly of the displacer above the high mercury level, said displacer comprising an inverted cupshaped portion equipped with a restricted gas vent and adapted when lowered to trap gas within said cup-shaped portion and force mercury in contact with said one electrode for al period corresponding to the rate of gas escape through said restricted gas vent but no longer.

6. In a mercury switch relay, the combinationl of a coil, a mercury switch associated with the coil comprising a switch envelope, a mercury illl, a displacer reciprocable within the envelope in response to the coil to displace more or less mercury according to the direction of movement, a gas illl, a plurality o! electrodes projecting into the envelope, one of which is positioned exteriorly of the displacer above the high mercury level, said displacer comprising an inverted cup-shaped portion equipped with a restricted gas vent and adapted when lowered to trap gas within said cup-shaped portion and force mercury in con tact with said one electrode for a period corresponding to the rate of gas escape through said restricted gas vent but no longer, the interior of the inverted cup-shaped portion of the displacer being in communication with the gas nll oi' the envelope when the displacer is in its raised position.

7. A mercury switch relay adapted to close an electrical circuit for a predetermined length of time in response to a relay coil. said relay comprising a coil, a switch envelope, a mercury flll, a displacer adapted to move in response to the coil to change the mercury level, a plurality of electrodes projecting into the envelope, one oi' which is positioned exteriorly of the displacer, a time delay element associated with the displacer adapted to retard the movement o! mercury away from one of said electrodes, the quantity of mercury comprising the illl in the envelope being such that with the mercury at rest in a position of equilibrium, the circuit through said one electrode and one other will be open regardless of the position of the displacer within the envelope.

8. In a mercury switch relay, the combination of a coil, a mercury switch associated with the coil comprising a switch envelope, a mercury nil, an armature adapted to move in response to the coil to displace more or less mercury according to the direction of movement, a gas ll, a plurality of electrodes projecting into the envelope, one of which is positioned above the high mercury level, and means for closing the circuit through said one electrode and one other for a predetermined time in response to said coil, said means including a time delay element adapted to yieldingly restrain a portion of the mercury tlll from reaching a podtion o! equilibrium with the remainder of the mercury iill whenever the amature is lowered.

CARL H. LARSON. 

